Telephone-exchange system.



E. E. CLEMENT. TELEPHONE EXCHANGE SYSTEM. APPLIOATIOH IILED NOV. 23,1906 RENEWED DEC. 81, 1010.

1,107,154. Patented Augi11,1914.

2 BHEETB-BBEET 1.

' Wilma:

Patented Aug; 11,191L

2 BKEETB SHEET 2.

noanroz ITED STATES PATENT OFFICE.

EIl'iJVARlD E. CLEMENT, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR,BY

liftESll'E ASSIGNMENTS, TO FREDERICK C. STEVENS, OF ATTIGA, NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Patented Au 11, 1914.

application filed November 23, 1905, Serial No. 288,776. RenewedDecember 31, 1910. Serial No. 600,278.

during the idle hour.

it is the primary object of my present invention to arrange a systemhaving mam and auxiliary switchboards, or what I may call main andequalizing switchboards, so

that individual overflow calls will be automatically trunked to theauxiliary board, and at a certain time, the chief operator or traliicmanager of the exchange may throw into operation all of the automaticdevices so that the entire load thereafter will be taken off the mainswitchboard and put on the auxiliary switchboard.

In carrying out my invention, 1 provide the usual line answering jacksand multiples if so desired, with cord-circuits and their equipment onthe main switchboard positions. In addition, I provide one or moreautomatic answering switches, which i call primary selectors, for eachposition, these being normally inactive, but capable of being renderedactive in any one of three ways. The first way is by means such as agrounding lug individual to each switchboard position, so that any oneor more positions can be plugged up to be handled automatically, whileother positions continue to "be handled manually. A second way ishyhaving a. controlling relay for each primary selector or group ofselectors, connectcd to talre current so that an excess of our rent dueto an excessive number of calls will energize said relay toautomatically render its prinuu'y selector active. The best form forthis I have found to be a solenoid, controlling the selector circuit,and itself con nected in the common return from the line lamps on itsposition. Such a solenoid can be adjusted with nicety, so that one, two,or more lamps can be permitted to light without working the solenoid;but the rise of current beyond one, two, three or whatever the number oflamps may be, due

to the lighting of additional lamps, that is to additional calls, willeffectively energize the solenoid, and so throw the overflow calls ontothe primary selector trunk and the auxiliary switchboard. The third wayis by having a series of relays, their contacts working in parallel withthe grounding plugs or their various positions, each relay controllingthe selectors on one position or one section of the switchboard, and allthe relays having their magnets in a common circuit leading to andcontrolled by the chief operator or traffic man, whereby at statedtimes, such as during the busy hour, or during the idle hour, all theprimary selector switches can be thrown in or can be thrown out at will.

The auxiliary switchboard in this system, which takes the overflowcalls, may have multiples of all the lines in the exchange, forconnective purposes, but I preferably provide it with automaticconnector switches containing line multiples, the auxiliary operatorshaving number senders in their cord-circuits, so that they may berelieved of the necessity for testing a line to ascer-. tain if it isbusy; for picking out the line and sticking the plug into its individualjack, and from ringing the wanted subscriber. These three demands beingeliminated, the auxiliary operators can handle almost twice as many.calls as they would if they had such demands to meet.

My invention is illustrated in the accompanying drawings, wherein-Figure 1 is a diagram of a subscribers station and a portion of the mainswitchboard, together with a trunk to the auxiliary switchboard. Fig. 2is a diagram co1nplementary to Fig. 1, showing the circuits of theauxiliary switchboard.

Referring to the drawings, A is one subscribers station, and A isanother, both equipped with the ordinary apparatus employed in commonbattery systems. These two stations are shown connected to a centraloflice in which operators connective circuits 0 are provided, each ofthese comprising the answering and calling plugs P, P, a listening andringing key not shown, answering and calling supervisory lamps s,

8 and controlling relays therefor, S

r and S"S Each cord-circuit is separated tery B is bridged across endthree insulated springs 79", 72

by a pair of condensers C, and the main batthe two ends as usual betweenthe pairs of relays, the two branches of the battery circuit being 1, 2,3 and 1, 41, 5. Further description of the ordinary cord-circuits is notthought to be neces Each line is equipped at the central ofiice with aline-relay M, a lamp signal'm, jacks J and a cut-cit relay N. These areall of a type and are arranged in a manner well understood by thoseskilled in the art. The

line G7 is normally connected to the linerelay M and ground, the relaybeing connected on its other side to the battery wire 1, connected tothe live side of battery B. When the cut-off relay N is energized theline is connected to the extensions 8-9 leading to the jacks, andsimultaneously to the extensions 8090 leading to individual contacts 79,p in an automatic primary selector switch P The peculiarity of thetwo-wire multiple circuit I have shown is that the cut-off relay N is inevery case energized over one side of the talking circuit, or thatportion thereof'leading to the connection terminals and normallydisconnected from the line. Hence this cut-off relay may derive currenteither from a cord- I circuit or from the battery connections throughthe circuit of the primary selector P The function of this primaryselector is to pick out and make connection with a calling line,plugging the same onto a trunk -11 leading to a jack J on an auxiliaryor equalizing section of the central ofi'ice switchboard, thereby doingautomatically what the operator does manually, when she trunks a call.The switch P is auxiliary to the operator O, and is intended to pick upcalls that the operator cannot handle and trunk them onto a' switchboardwhere they can be handled. It comprises a spindle 79 which may either beconstantly rotating or intermittently rotated as required. The lattercondition is preferable because of the economy in power. The spindlecarries an electromagnct shell p having on its upper head a tube 7? inwhich a plug 72 is fitted to slide, and as the spindle turns, the shell,tube and plug all turn with it, being engaged together by the armaturep, which is carried on the shell and which has a stud 7/ taking into'anotch in the collar fixed en the spindle 79 when the armature isretracted. The armature has an upwardly extending lever 79 which carriesat its lower 79, and at its upper end extends through a slot in theunderside of a tube 71 to engage the plug 79", whereby as the armatureis attracted upwardly by the magnet the plug will be shot out radiallyfrom the spindle. The armature 1) has a central perforation throughwhich the spindle passes, and the magnet structure is supported on thespindle by means of a split collar 39", which takes into an annulargroove in the spindle and turns freely therein. Around the spindle is acontinuous ring of what I may denominate line answering jacks J Each ofthese comprises a pair of line springs 11, p, a local test or callcontact 72 and a pair of trunk springs 72 -7). In addition to these, Iprovide a pair of continuous contact rings p", p, which extend entirelyaround the circle of jacks, afiording constant connection through thesprings p, p with windings of magnet p. This magnet 79'' has twowindings, one connected at one end to the spring 1) and at the other endto the spring 72 through the wires 12 and 13, respectively; and theother winding connected from thespring 29 on one side to the shell ofthe magnet and thence to the spindle, which is grounded as shown, on theother side. These two windings are indicated diagrammatically in dottedlines, in Fig. 1. The first, which I have marked 14: in the figure, isthe energizing winding which responds to the call of a subscriber andstops the switch, shooting the plug p into his line-jack J 2 when thespring 79 rests on his contact The other winding 15 is what I shall callthe holding or controlling winding, being connected back through thewire 16 to the spring 79 through the ring 71 to the wire 17, which iscarried along with the trunk wires 10, 11 and terminates on the frontcontacts of the relays S" and S.

The relays S and S are bridged across the trunk 1011 just as the relaysS, S are bridged across the operators circuit, with the main battery Bbetween them, the circuit being: B, 1, 18, 19, S 20, 10, and from theother side: 11, 21, 22, 23, and ground. The wires 18 and 19, and thewires 22 and 23 are normally joined through the back contacts of therelay S, this relay itself beng included in a wire 24 leading to thesleeve contact of the trunk jack J on the auxiliar" swirhboard. The twosprings of this jack constitute terminals of the trunk wires 10, 11, andthe jack has associated with it a signal lamp m connected on one side toground and on the other through wire 25 to front contact of relay SThus, it will be observed the locking circuit of the switch P iscontrolled by either or both of the coils S", S, while the lamp circuit25 is controlled by the relay S and this in turn by the relay S.

The most essential feature of the invention is now reached. This is thecontrol of the energizing coil 14 in the primary selector P so thatnormally it will be inactive and irresponsive to line calls, but it maybe rendered active and responsive when occasion demands. This coilterminates at one end, as I have said, on the spring p, which is beingcarried constantly around over the line contacts 7), so that if a lineis calling and its relay M by pulling up has raised the potential of thecontact p, current may be taken through the wire 27, contact 2, andspring 7)", by the coil 14, provided that the coil has a ground on theother side. This is the point. The other side of the coil terminates onthe spring 7), and this is constantly in contact with the ring 39 whichI may term the ground ring. If this ring is grounded the coil 14 will beenergized to plug in on the jack J of a calling line. Otherwise not.There are three ways in which this rin may be grounded, which I haveillustrated in Fig. 1. The first of these is by ground plug X, which hasa metal head adapted to be inserted in a jack to bridge the contactsthereof and so put ground on the wire 28. The second way is by means ofa ielay or ground switch X, whose circuit 29 is controlled by a key Kadapted to be manipulated by the chief operator or traflic manager. Ihave shown three of these relays, controlling respectively groundbranches 30, 31 and 32 supposed to lead toprimary selectors P at thesame or at different positions. The idea is that the trafi'ic man mayrender one or all of these switches permanently active by closing theswitch K. If selection is to be had, that is if some selectors are to bethrown in and others not, then I may provide a regular set of groundwires 30, 31, 32, etc.,'leading to strips on a simple switchboard whichcan be plugged up to ground by the traflic manager in any desired orderor combination. I do not limit myself either to the relays X or theequivalent switch device, however, as any switching means maybe'employed which will give the proper control over the grounding of theseveral selector wires 28 and their ground rings 3).

The third way in which the ring may be grounded is by means of the relayX automatically controlled, and set to respond when the work on itsposition reaches a certain predetermined point. I have shown this relayas a solenoid with its winding connected in the common return .33 fromthe line-lamps m, m, m on the position to which the selector P isappropriated and connected. This solenoid has a core 0: which isnormally down, and which will not pull up without a certain definiteamount of current, this being determinable by the winding of thesolenoid and the weight applied on the core. It may be assumed that thesimultaneous lighting of three lamps will not pass sufficient current toeffectively energize the solenoid, but if an additional lamp lights, theextra current which thus passes will cause the solenoid to pull up itscore, closing the branch 34 on .the ground wire 35, and thus puttingground on the rin 1) through the wire 28.

uppose that We have ten pairs of cords and plugs O, and three primaryselector switches P assigned to each position, then the solenoid X wouldcontrol the ground wire 28 for the three selectors, P of its position,and would render the active by grounding their rings 79 whenever thereare more than three lamps burning on the position at once, a conditiondue it is to be supposed to the overloading of the operator. Theadditional calls will thus be picked up by the primary selectors andautomatically trunked to the auxiliary switchboard, whereby lamps wewill light for line signals, and these overflow calls will be handled bythe auxiliary operators in the ordinary way.

The idea of providing individual grounding plugs X, is to permitindividual positions to be vacated by their operators and plugged up tothe automatic selectors. When the load drops somewhat, it is thuspossible to take off a portion of the operators, to plug up the selectorswitches at their positions, and thus to divide the work between themain and auxiliary boards. As I have stated, all these ground plugs Xmay be grouped under the control of the trafi ic manager or chiefoperator.

The idea of providing the relays X or their equivalent switches is toenable all of the primary selectors in the central oiiice to be renderedactive at once, which will occur when the entire load or a largeproportion thereof is to be handled on the auxiliary board. I

The solenoid X need not be included in the direct path of the currentfrom the lamps m, m, m, etc'., but may be shunted by such a resistanceas will permit a suitable portion of the current to pass the solenoid,and yet will maintain an independent path to ground for the lamps, incase of any accident to the winding.

Before I take up Fig. 2 for description, I will first briefly point outthe essential mechanical {features of the typical automatic connectorswitch. The use of this switch with the system shown in Fig. 1 is not atall obligatory. In fact, so far as the main essential features of thepresent invention-go, they are all shown in Fig. 1.

That is to say, the jacks J may be located on the auxiliary switchboardas answering jacks in the usual manner, with their line lamps m closelyassociated with them, and above them may be placed multiple panelscontaining multiple jacks of all the lines in the exchange. With such anarrangement the auxiliary board would be similar in its appearance andoperatlon to every other sectlon of the mam exchange switchboard.

The only difference-would be that whereas upon any given position at anordinary section of the main switchboard, the subscribers operator couldidentify the jacks J as belonging to individual subscribers, upon theauxiliary positions the pperators could identify the jacks J only asassociated with individual positions of the main board, for obviouslyany subscribers line rangement upon both the main and auxiliaryswitchboard sections would be that any operators could be assigned toany positions of either board without varying their work and without thenecessity of teaching them any new methods of operating. However, in thepresent case as in the companion application, filed November 21, 1905,Serial No. 288,369, I include semi-automatic features, shown in Fig. 2,in order to expedite the work of the, auxiliary operators,

and to simplify theparts exposed to wear on the auxiliary board, whichwill have to be renewed much more frequently than any other part of theswitchboard equipment, since according to my invention it remains inservice continuously, and for a great part of the time is worked to itsmaximum limit. I consider it one of the most valuable features of myinvention thus to concentrate depreciation and wear upon a definite unitof switchboard which can be rebuilt without changing the mainswitchboard.

The automatic connector switch F which is illustrated diagrammaticallyin Fig. 2 is of the general type described in the patent to Keith andErickson 815,176, of March 13, 1906. It comprises a spindle f bearingwipers f adapted to engage contacts 7. The spindle may be stepped upvertically by means of the vertical magnet f and may also be rotated bymeans of the rotary magnet f Circuits of the various parts of the switchare regulated by a side switch com prising switch arms f and 7 7' and f.

These arms are all moved together on a common pivot and are setback tozero, that is, in the position shown in Fig. 2,'when the switchingmechanism is released, in the manner hereinafter set forth.

Referring now to the diagram in Fig. 2, the arrangement of the switch Fwill be rstood from the foregoing statement, in connection with thefollowing: The ma ae c 7", f and f are controlled by the relays f and fThe side switch magnet f is controlled by the rotary relay f Magnets fand f are merely bridging magnets or choke coils, across the calling endof the switch trunk, included in the connection 30, 31, of the mainbattery B, through which talking current is supplied to the calledsubscriber. The vertical and ro tary relays f and f are permanentlybridged on the answering end of the switch trunk, which is separatedfrom the calling end by the condensers G. g is the ringing relay,connected to the last contact point of the sideswitch-arm f on one side,and to the battery wire 32 on the other. f, as already stated, is therelease magnet, controlled by the relay f which in turn has its circuitclosed in either one of two ways, first by both the relays f and f beingonergized at once; second, by being connected to the second point of theside switclrarni f by the relay f" and in response to the last rotaryimpulse for testing the line wanted after it has been selected.

P and P are the answering and calling plugs, respectively, of a pair onthe auxiliary board, connected by theconductors 33, 34, 35 and 36, whichinclude the condensers C. The plug P has three contacts, a tip, ring andsleeve, marked 2, p, 19 The tip and ring are connected to the wires 33and 35, while the sleeve is connected through wire 37 to a cut-off orrelease relay F, the armature is shown as grounded, and normally restingagainst the terminals of the wires 38 and 39, which are tapped onto thecord-conductors 34 and 36.

Associated with the calling plug I is a sender, or number transmitter,which I have indicated diagrammatically at with a spindle 0, carryingteeth 0' and 0 coiiperating with springs 0 these springs being connectedthrough wires 40 and 41 with the two cord-conductors 34 and 36, and thespindle being grounded through the wire 42. In operating this form ofsender the button 0 is pressed down, and a pin 0 passing into a slot 0in the tubular upperend of the spindle 0, turns the latter so that theteeth 0 do not touch the springs 0 in going down. In coming back,however, the inner spindle carrying the button 0" is pressed up by asuitable retracting spring not shown,

and its first movement upward turns the sleeve back so that the teeth 0and 0 turn into contact with the springs o I do not of course limitmyself to the use of this special sender. as any suitable type may beemployed. The idea is that by pressing down the button a greater or lessdistance any number of impulses up to ten may be sent by the teetlrocontacting with the spring 40, and always at the end of every set ofsuch impulses a single impulse will be sent by the one tooth 0.

In a cord-circuit of Fig. 9., the relays S'" and S correspond preciselyto the relays S and S in Fig. 1. They jointly control the supervisorylamp s and this lamp indicates to the auxiliary operator when thecalling subscriber has hung up, the control of the connection beinggiven to him. Whenthe plug P is thereupon pulled out from the pol: J,the relay F lets go and grounds both cord-conductors 34 and 36, therebyenergizing both relays f and f of the automatic switch F, whichenergizes the release relay f and the release magnet f, to restore theswitch.

With the cord-circuits of .plu s P, P, described, the automatic switchreleased and restored until the auxiliary operator has actually pulledthe plug P. I have shown a second cord-circuit in Fig. 2, however, inwhich the calling subscriber is enabled to release the switch F himself,by momentarily or permanently hanging up his receiver. This isparticularly useful where the calling subscriber desires to make animmediate recall, that is another call for another connection. In suchcase, with the circuits previously described he would either hang upuntil the operator had pulled, the plug P, which he would have no meansof knowing, or he would announce to theoperator that he desired arecall, by moying his switch-hook up and down to make and break hiscircuit, and thereby flash the lamp Then the operator, perceiving thislamp to flash, would restore the switch F by pulling the plug P-*, butwould immediately go back again to the jack with the same plug, comingin with herlistening key at the same time and asking for the new numberwanted. With the second cord-circuit, having the terminal plugs P and P,the op rator need not pull either plug, but in response to the flash ofthe supervisory lamp she simply comes in on her listenin key 'and getsthe new number Wanted. If this number is in the same hundred as the lastone called, she leaves the plug 1? in the jack J 4 and picks out the newsubscriber by manipulating her button 0 as before. If the new subscriberwanted is in another hundred, she shifts the plug P to ajaek J 4 of thathundred, and then manipulates the button 0 to send the required tens andunits digits.

In order to avoid the necessity for pulling the plug P to restore theswitch F, I take the return wire 370 from the magnet F, and instead ofconnecting it directly to the battery, as in the cord-circuit 1, P, Icarry it to a front contact of the relay S The re sult is that when thesubscriber desiring a recall vibrates his switch-hook, the magnet F willvibrate as therelay S vibrates its armature, and simultaneously with theflashing of the lamp The vibrations of the relay F will put ground onthe conductors 38 and 3S) repeatedly, so that the relays f and f willpull up to closethe circuit of the release relay f and thereby actuatewill not be the four that are unattended to.

the release magnet f. The automatic switch F being thus restored,obviously the operator need only ask what number is again required. Atthe same time, it will be observed that the operator also has control ofthe automatic switch F, so that the called subscriber cannot beindefinitely hung up or locked out through accident or malice on thepart of the calling subscriber. If the lamp 8 does not light, but theconnection remains up an unreasonable time, the operator pulls the plugP and the switch F is at once released.

The operation of my system will be understood from the foregoingdescription, but I will briefly trace one connection through its varioussteps, pointing out the methods of handling the call upon the main andmixiliary switchboards. .lVe will assume that subscriber A desires totalk to subscriber A. He takes down his receiver, his relay M lights thelamp m, and if none of the auxiliary contrivances are in use, theoperator 0 in Fig. 1 will answer the call and complete the connection inthe ordinary way with plugs P, P. Assuming next that the solenoid relayX is in servlce, as shown in Fig. 1, let us assume also that there arethree calls unattended to ahead of A, that is there are three lampsburning, with which his lamp makes four. Current through the three lampsalready burning was insuiticient to pull up the solenoid core,'butimmediately upon the relay M pulling up to light the lamp m, theadditional current in return wire will effectively energize thesolenoid, and a circuit is partially completed for the energizing coil14 of the primary selector P, as follows: ground, 35, 34, 28, p 72, 13,14, 12, p. The switch spindle, in turning carries the spring p oversuccessive contacts 79 until it comes to one of This may not be thecontact of subscriber A, but it 7 will be. some one of the four. Upontouching this, the circuit of energizing coil 14 is completed throughthelive contact 7) and wire 27 to the front contact of relay M and tobattery wire 1, battery 13 andground. The coil 14 thereuponef'ectivelyenergizes the coil and shell of the magnet 79, pulls up the armature p,and thereby simultaneously uncouples the magnet from the spindle andpushes the plug 72" into the jack J spreading apart the springs 79, 29",causing them to make contact with springs p, 7). I should here statethat the springs 29, 72 all around the circle are connected together.Theinstant plug 7f is inserted, the trunk circuit 10 11 is connected tothe line conductors 80-90,an(l a circuit for the cut-oil relay N isestablished as follows: B, 1, 18, 19, C 20, 10, 79 y), 80, 8, N andground. The relay N then cuts oil the magnet M, which in turn cuts oflthe lamp m and the wire 27 from thebattery, and the contact 29 becomesand puts battery on the wire 17, so as to feedcurrent back to thewinding 15 of the selec- W h PT", as follows: B, 1, 18, 26, 260,

16, 15 and armature of S, P P

ground through the frame of the switch.-

The movement of the plug 12 and its asso;

ciated parts are sluggish, due to friction and inertia, hence the verybrief interval of time:

which elapses between the cutting off of current from the winding 14 andthe cutting on of current through the winding 15 18 m-- suflicient topermit the retractlou of the plug, which remains held in the jack J 2as" long as current is supplied to the wire 17.- Tlierelay'S being inthe path of current through the sleeve side of the trunk, pulls, up, andlights the lamp wa associated Wltll the 'jackJ on theauxiliary"'switchboard,f

through the following circuit:;fl3,'l, 18, 26,;

armature of S 25, m and ground. Thus the instant the plug 10 cuts intothe linejack J and the lamp m of the main switchboard isexjtinguished,the call is simultaneously transferred to the lamp 'm, on the auxiliaryswitch-board. It is perhaps unnecessaryfor me to point out at this stagemore than I have already done the use of the relays X or the'plugs X, ingrounding the wire 28 when thesolenoid X is either out of service, ornot present. I have assumed a condition where -a plurality of line lampssimultaneously burn on the main switchboard, but of co urseit may bedesired to render the selector switch P active when no lampsare"burning,or an insuflicient number to energize solenoid X In thenight hours for instance, when it' is desired to dispense with theold-fashioned patrol, the switch K may .be' closed and all the selectorswitches P ln the central oflice thereby rendered active, leaving these,switches the sole means of picking up and connecting callingsubscribers on all parts of the main switchboard. With verylightbusiness a single operator at the" auxihary board will thus have all the'busine'ss brouglit to her, and that without any perceptible loss oftime.

I have statedlth'at there may and preferably will be a plurality ofswitches P, P for each position. The tubes and springs of theseswitches'and the' notches which take their studs. 29 are set indifferentannular positions around the spindle "p lVhere three switches are setupon one spindle, they would be 120 degrees apart, and assuming onehundred line-contacts per switch,

each line having its contacts passed? over three times in a revolutionof the spindle,

by the three springs p of the three switches,

the longest timethat need-elapse'between thecall and the sticking of theplug p wis.

a very small fraction overone second. It

has beenfound in. practice that switches of this character can be reliedupon to test fifty contacts per second, with careful adjustment, and, asthe above stated figure would require the testing of only about thirtyper second, it is believed to be conservative.

The reason for this quick action is that the first movement of thearmature p uncouples the magnet-from the spindle, and as the parts arebalanced and the peripheral speed of rotation of the tube p3 is. lessthan i three inches per.- second, there is so little effective momentumthat it is negligible.

In cases where the force is beingreduced on the mainboard, or. where.forany, rea-.

son part of the operators are withdrawn, a

plug or plugsX maybeused to. ground the wire28. The lamp wa indicatingacall on-the auxiliary switchboard, ifthat' switchboard be equipped withmultiple-contacts, etc., the

operator 0 inserts, tests, connectsand rings off in ,a well-knownmanner. If,.however, the board 1S equipped as shown 111,

Fig. 2 with semi-automatic apparatus, the operation then proceeds asfollows: The

plug P is inserted in thejack J, and current at once flows by thefollowing pathz.

B (Fig. 2), 370, s 35, 10, so, a, cut-oif relay N and ground. It alsoflows through 370,1 37, 79 J, 24, S and ground. a The I relays F and Sare thereupon energized. F HTQIDOVGS the ground from wires 38 and 39. Scuts ofi the relays S and S, andsimultaneously puts battery on the wire17 to pull up the selector switch I, as follows: B, 1, 18, 17, 7)", 7216, .15 and ground through the frame of the switch. Up to this pointtheswitch l? was controlled by the calling subscriber, andif he had hungup, so that relay S had lost current, ,he would have released it, butnowthe relay S takes control, and itin. turn held up over the wires 243'7,'whosecontinuity is determined by the operator 0 in Fig. 2. The

operator 0 being thus connected with the calling subscriber, comes in.through her listening key on the cord conductors 33-35 and gets thenumber wanted,- ,We will assume this to be i l- 68, the number ofsubscriber A, for instance. The operator inserts the plug P in thejaclrJ of group No. 44, all 'of. which have trunks l3-44; leading toautomatic switches F, in which are found multiple terminals f (seeFig. 1) of subscribers lines numbered from 4400 to The operator thenpushes down button 0 so that six teeth pass the springs o, andiureturningthese send six impulses its tip side eit 'S, S or S of acord-circuit. Such a on in place of the vertical magnet-f The operatorthen sends the final number 8' in the same manner, and the magnet turnsthe wipers f around to contacts No. 8,

which being in the 6th row belong to line N o. 68, and these being in aNo. 44 switch, the whole number of the line is 4468. If the line is busythere will be a ground on er through a magnet f of an automatic switch,or through a relay I round will complete a circuit through t e ti wiperthe arm f, the contacts 53, and the re ay f when the last rotary impulsedue to the tooth 0 f" is thereby energized. The completion of thiscircuit will energize magnet f to release and restore the switch. Ifthere be no ground on the tip side of the wanted line, however, thistest circuit will not be completed, and the switch wipers will remain onthe line contacts. The operator may then ring the wanted subscriber bymoving the button 0 up and down indiscriminately, or she may be providedwith a key to ground the conductor 34, which is the preferablearrangement. Upon the completion of the conversation, if the cordcircuitP P be used, the lamp 8 lights when the calling subscriber hangs up, andthe operator pulls the plugs, always pulling the plug P first. Thisbreaks the continuity of wires 2437 and releases the relays S and F. Theformer takes battery off wire 17, and as the relay S remains deenergizedowing to the subscriber A having hung up, the switch I gets no current,its armature p is retracted to recngage the stud with the notch in itscollar, and the switch resumes its round of testing. ()n the other handthe second relay F grounds the wires 38 and 39 simultaneously, whichenergizes both relays f and f sinn'lltaneously, which closes the circuitof the release relay f which closes the circuit of the release magnet f,and finally this releasesthe switch, which re turns to zero or normalposition. If the cord-circuit P P be used, the switch .F is released assoon as the calling subscriber hangs up or flashes his lamp 8. Vith thisexception the operation is the same as in the other case.

Having thus described my what I claim and ters Patent is:

1. In a telephone exchange system a main switch board, a plurality ofsubscribers is sent, and magnet invention, deslre to secure by Letlinesconnected thereto, operators connective devices on the main board, anauxiliary switch board and trunk connections therefrom with terminalautomatic selective answering switches, multiple connections from thesubscribers lines to the banks of said switches, and means associatedwith the subscribers lines to determine the activity or non-activity ofsaid automatic switches, and thereby to determine the answering of thecalls on the main or auxiliary board.

2. In a telephone exchange system a main switchboard, an auxiliaryswitchboard, means for normally receiving and answering calls on themain switchboard, automatic means for receiving and transferring callsby connecting the calling lines to the auxiliary switchboard, and meanscontrolled in the operation of the main switchboard apparatus todetermine such transfer of calls to the auxiliary board. M

3. In a telephone system a main switchboard having answering positionsand submary selector switch associated with each position and containingterminals of the lines thereat, a trunk line from each primary selectorswitch to an auxiliary switchboard, with answering terminals thereon,and means to determine the activity of the primary selector switches inaccordance with the condition of the load on the main switchboard.

4. In a telephone system a main switch-v board having answeringpositions and subscribers lines apportioned to each, a pri- -maryselector switch associated with each position and containing terminalsof the lines thereat, a trunk line from each primary selector switch toan auxiliary switchboard, with answering terminals thereon, and meansactuated by a predetermined increase in the load on any position of themain switchboard to render the corresponding primary selector switch orswitches active.

5. In a telephone system a main switchhoard having answering positionsand subscribers lines apportioned to each, a primary selector switchassociated with each position and containing terminals of the linesthereat, a trunk line from each primary selector switch to an auxiliaryswitchboard, with answering tcrminals thereon, and means controlled bythe subscribers in calling to render the primary selector switchesactive when a predetermined number of calls remain unanswered on themain switchboard.

6. In a telephone system a main switchboard having answering positionsand subscribers lines apportioned to each, a primary selector switchasociated witheach position and containing terminals of the .linesthereat, a trunk line from each priscribers lines apportioned to each, aprimaryselector switch to an auxiliary switchboard, with answeringterminals thereon, and arelay connected to be controlled by current dueto subscribers, calling so as to render a primary selector switchorswitches active, when a predetermined number of subscribers calls areunanswered on the main board. I v

7. In atele hone exchange system a main switchboard lgavingsubscribersline-terminals and lineisignals, an automatic primary 8. In a telephoneexchange system, a plu ralityof subscribers lines: and a plurality ofswitching means to interconnect the same,

multiplejconnections from the lines to the several switching means, andcontrolling devices responsive to fluctuations in the calling load,adapted to determine the particular switching means to be used for anypartlcular connection desired.

9. In a telephone exchangesystem, a manual switchboard and automaticswitching devices, a plurality of subscribers lines having multipleterminals in both, and

means determined by load conditions to switch the lines for conversationthrough 7 either.

Copies of this patent may be'obtained for 10. In a telephone exchangesystem, a plurality of subscribers lines, a main manual switchboard forinterconnecting the lines, and an auxiliary switchboard therefor withautomatic answering means'and' automatic control.

11. In a telephone exchange system, a pluralit'y' of subscribers lines,a main manual switchboard for interconnecting the lines forconversation, and an auxiliary switchboard also adapted to interconnectthe lines and automatically controlled by current changes due to callingload changes on the main switchboard. a I

12. In a telephone exchange system, a

plurality of subscribers lines, a main switchboard provided with manualconnective apparatus, an auxiliary switchboard provlded with automaticanswering sw tchmg means, and means at said'cen'tral station fordetermining the furtherance of a desired connection either through saidmanualconnective means or through said automatic switching means andindependently 'of the manual connective means. A

13. In a telephone exchange system, a

plurality of subscribers lines, a' main switchboard provided with manualcon -nective apparatus for normally inter'con- 'necting the lines, anauxiliaryswitchboard provided with automatic switches and meansconnection for automatically effecting through said switches asdetermined-bythe number of calls.

In testimony whereof I afiix my signature in presence of two witnesses;

EDWARD E.

Witnesses E. EoMoNs'roN, Jr., JAMES H. MARK.

five cents each, by addressing the Commissioner of Patents, Washington,G.

